1. Field of the Invention
The present invention relates to an improved electric dc motor operated gear rotor pump mainly adapted for automobile fuel injection system, and more particularly to a floating coupling device adapted for use in connection of the driving shaft of a dc motor to an inner rotor of a gear rotor pump which is rotatably operated on a fixed shaft. The coupling device according to the present invention is made of either plastics or metals. As a result of the independent, unsupporting relation between the driving shaft of the dc motor and the fixed shaft of the inner rotor, the axial alignment of the above identified two shafts in assembly is not necessarily required, i.e., excessive precision in machining can be avoided, resulting in the reduction of production cost. However, the present invention can perform as satisfactorily as those previous pumps with even less noise.
2. Description of the Prior Art
There have been many types of fuel pumps designed to supply fuel to internal combustion engines of automobiles, such as cam-operated diaphragm pumps and positive displacement vane type pumps. However, another well known gear rotor type pump has been widely adopted in the newly developed fuel injection system for auto gasoline engines popularly employed in gas-saving cars recently manufactured.
Generally speaking, a vane type pump does not have the problem of axial alignment in assembly, but it produces more noise than a gear rotor type pump which requires axial alignment. The advantage of the latter is that less noise is produced in operation.
Tuckey's U.S. Pat. No. 4,500,270 disclosed a fuel pump of gear rotor type operated by a specially modified dc motor which has a cylindrical drive projection 42 at one end with slender projecting fingers 44 circumferentially spaced around projection 42. Those projecting fingers must be fitted into a number of axial deep holes 155 spaced on the inner gear around a circular periphery thereof. Thus, the dc motor can accordingly drive the gear rotor pump to work by moving the inner gear rotatably against an outer gear so to pump fuel from a remotely located tank to a combustion engine.
Although, the Tuckey's U.S. Pat. No. 270' can work normally well, there are still a number of disadvantages in view of production cost and precision machining of the elements and the assembly speed.
The dc motor of Tuckey's, 270' patent adopts a modified cylindrical drive projection having slender projecting fingers. The structure thereof is different from common dc motor of the prior arts; therefore, the production cost unavoidably is increased. Besides, the fitting of the plurality of slender projecting fingers into the axially disposed deep holes requires releative precision in the alignment therebetween.
To solve the above cited problems the present inventor has worked out an improved floating coupling device which is disposed between a dc motor and a gear rotor pump with one end in detachable engagement with the driving shaft of the motor and the other end also in detachable engagement with the inner rotor of the gear rotor pump; thereby, axial alignment is not required in assembly and the operation noise can be also reduced.